1 //===- LexicalScopes.cpp - Collecting lexical scope info ------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements LexicalScopes analysis.
11 //
12 // This pass collects lexical scope information and maps machine instructions
13 // to respective lexical scopes.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/CodeGen/LexicalScopes.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineInstr.h"
20 #include "llvm/IR/DebugInfo.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Support/ErrorHandling.h"
24 #include "llvm/Support/FormattedStream.h"
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "lexicalscopes"
28 
29 /// reset - Reset the instance so that it's prepared for another function.
30 void LexicalScopes::reset() {
31   MF = nullptr;
32   CurrentFnLexicalScope = nullptr;
33   LexicalScopeMap.clear();
34   AbstractScopeMap.clear();
35   InlinedLexicalScopeMap.clear();
36   AbstractScopesList.clear();
37 }
38 
39 /// initialize - Scan machine function and constuct lexical scope nest.
40 void LexicalScopes::initialize(const MachineFunction &Fn) {
41   reset();
42   MF = &Fn;
43   SmallVector<InsnRange, 4> MIRanges;
44   DenseMap<const MachineInstr *, LexicalScope *> MI2ScopeMap;
45   extractLexicalScopes(MIRanges, MI2ScopeMap);
46   if (CurrentFnLexicalScope) {
47     constructScopeNest(CurrentFnLexicalScope);
48     assignInstructionRanges(MIRanges, MI2ScopeMap);
49   }
50 }
51 
52 /// extractLexicalScopes - Extract instruction ranges for each lexical scopes
53 /// for the given machine function.
54 void LexicalScopes::extractLexicalScopes(
55     SmallVectorImpl<InsnRange> &MIRanges,
56     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
57 
58   // Scan each instruction and create scopes. First build working set of scopes.
59   for (const auto &MBB : *MF) {
60     const MachineInstr *RangeBeginMI = nullptr;
61     const MachineInstr *PrevMI = nullptr;
62     const MDLocation *PrevDL = nullptr;
63     for (const auto &MInsn : MBB) {
64       // Check if instruction has valid location information.
65       const MDLocation *MIDL = MInsn.getDebugLoc();
66       if (!MIDL) {
67         PrevMI = &MInsn;
68         continue;
69       }
70 
71       // If scope has not changed then skip this instruction.
72       if (MIDL == PrevDL) {
73         PrevMI = &MInsn;
74         continue;
75       }
76 
77       // Ignore DBG_VALUE. It does not contribute to any instruction in output.
78       if (MInsn.isDebugValue())
79         continue;
80 
81       if (RangeBeginMI) {
82         // If we have already seen a beginning of an instruction range and
83         // current instruction scope does not match scope of first instruction
84         // in this range then create a new instruction range.
85         InsnRange R(RangeBeginMI, PrevMI);
86         MI2ScopeMap[RangeBeginMI] = getOrCreateLexicalScope(PrevDL);
87         MIRanges.push_back(R);
88       }
89 
90       // This is a beginning of a new instruction range.
91       RangeBeginMI = &MInsn;
92 
93       // Reset previous markers.
94       PrevMI = &MInsn;
95       PrevDL = MIDL;
96     }
97 
98     // Create last instruction range.
99     if (RangeBeginMI && PrevMI && PrevDL) {
100       InsnRange R(RangeBeginMI, PrevMI);
101       MIRanges.push_back(R);
102       MI2ScopeMap[RangeBeginMI] = getOrCreateLexicalScope(PrevDL);
103     }
104   }
105 }
106 
107 /// findLexicalScope - Find lexical scope, either regular or inlined, for the
108 /// given DebugLoc. Return NULL if not found.
109 LexicalScope *LexicalScopes::findLexicalScope(const MDLocation *DL) {
110   MDLocalScope *Scope = DL->getScope();
111   if (!Scope)
112     return nullptr;
113 
114   // The scope that we were created with could have an extra file - which
115   // isn't what we care about in this case.
116   if (auto *File = dyn_cast<MDLexicalBlockFile>(Scope))
117     Scope = File->getScope();
118 
119   if (auto *IA = DL->getInlinedAt()) {
120     auto I = InlinedLexicalScopeMap.find(std::make_pair(Scope, IA));
121     return I != InlinedLexicalScopeMap.end() ? &I->second : nullptr;
122   }
123   return findLexicalScope(Scope);
124 }
125 
126 /// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
127 /// not available then create new lexical scope.
128 LexicalScope *LexicalScopes::getOrCreateLexicalScope(const MDLocalScope *Scope,
129                                                      const MDLocation *IA) {
130   if (IA) {
131     // Create an abstract scope for inlined function.
132     getOrCreateAbstractScope(Scope);
133     // Create an inlined scope for inlined function.
134     return getOrCreateInlinedScope(Scope, IA);
135   }
136 
137   return getOrCreateRegularScope(Scope);
138 }
139 
140 /// getOrCreateRegularScope - Find or create a regular lexical scope.
141 LexicalScope *
142 LexicalScopes::getOrCreateRegularScope(const MDLocalScope *Scope) {
143   if (auto *File = dyn_cast<MDLexicalBlockFile>(Scope))
144     Scope = File->getScope();
145 
146   auto I = LexicalScopeMap.find(Scope);
147   if (I != LexicalScopeMap.end())
148     return &I->second;
149 
150   // FIXME: Should the following dyn_cast be MDLexicalBlock?
151   LexicalScope *Parent = nullptr;
152   if (auto *Block = dyn_cast<MDLexicalBlockBase>(Scope))
153     Parent = getOrCreateLexicalScope(Block->getScope());
154   I = LexicalScopeMap.emplace(std::piecewise_construct,
155                               std::forward_as_tuple(Scope),
156                               std::forward_as_tuple(Parent, Scope, nullptr,
157                                                     false)).first;
158 
159   if (!Parent) {
160     assert(
161         DISubprogram(cast<MDSubprogram>(Scope)).describes(MF->getFunction()));
162     assert(!CurrentFnLexicalScope);
163     CurrentFnLexicalScope = &I->second;
164   }
165 
166   return &I->second;
167 }
168 
169 /// getOrCreateInlinedScope - Find or create an inlined lexical scope.
170 LexicalScope *
171 LexicalScopes::getOrCreateInlinedScope(const MDLocalScope *Scope,
172                                        const MDLocation *InlinedAt) {
173   std::pair<const MDLocalScope *, const MDLocation *> P(Scope, InlinedAt);
174   auto I = InlinedLexicalScopeMap.find(P);
175   if (I != InlinedLexicalScopeMap.end())
176     return &I->second;
177 
178   LexicalScope *Parent;
179   if (auto *Block = dyn_cast<MDLexicalBlockBase>(Scope))
180     Parent = getOrCreateInlinedScope(Block->getScope(), InlinedAt);
181   else
182     Parent = getOrCreateLexicalScope(InlinedAt);
183 
184   I = InlinedLexicalScopeMap.emplace(std::piecewise_construct,
185                                      std::forward_as_tuple(P),
186                                      std::forward_as_tuple(Parent, Scope,
187                                                            InlinedAt, false))
188           .first;
189   return &I->second;
190 }
191 
192 /// getOrCreateAbstractScope - Find or create an abstract lexical scope.
193 LexicalScope *
194 LexicalScopes::getOrCreateAbstractScope(const MDLocalScope *Scope) {
195   assert(Scope && "Invalid Scope encoding!");
196 
197   if (auto *File = dyn_cast<MDLexicalBlockFile>(Scope))
198     Scope = File->getScope();
199   auto I = AbstractScopeMap.find(Scope);
200   if (I != AbstractScopeMap.end())
201     return &I->second;
202 
203   // FIXME: Should the following isa be MDLexicalBlock?
204   LexicalScope *Parent = nullptr;
205   if (auto *Block = dyn_cast<MDLexicalBlockBase>(Scope))
206     Parent = getOrCreateAbstractScope(Block->getScope());
207 
208   I = AbstractScopeMap.emplace(std::piecewise_construct,
209                                std::forward_as_tuple(Scope),
210                                std::forward_as_tuple(Parent, Scope,
211                                                      nullptr, true)).first;
212   if (isa<MDSubprogram>(Scope))
213     AbstractScopesList.push_back(&I->second);
214   return &I->second;
215 }
216 
217 /// constructScopeNest
218 void LexicalScopes::constructScopeNest(LexicalScope *Scope) {
219   assert(Scope && "Unable to calculate scope dominance graph!");
220   SmallVector<LexicalScope *, 4> WorkStack;
221   WorkStack.push_back(Scope);
222   unsigned Counter = 0;
223   while (!WorkStack.empty()) {
224     LexicalScope *WS = WorkStack.back();
225     const SmallVectorImpl<LexicalScope *> &Children = WS->getChildren();
226     bool visitedChildren = false;
227     for (SmallVectorImpl<LexicalScope *>::const_iterator SI = Children.begin(),
228                                                          SE = Children.end();
229          SI != SE; ++SI) {
230       LexicalScope *ChildScope = *SI;
231       if (!ChildScope->getDFSOut()) {
232         WorkStack.push_back(ChildScope);
233         visitedChildren = true;
234         ChildScope->setDFSIn(++Counter);
235         break;
236       }
237     }
238     if (!visitedChildren) {
239       WorkStack.pop_back();
240       WS->setDFSOut(++Counter);
241     }
242   }
243 }
244 
245 /// assignInstructionRanges - Find ranges of instructions covered by each
246 /// lexical scope.
247 void LexicalScopes::assignInstructionRanges(
248     SmallVectorImpl<InsnRange> &MIRanges,
249     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
250 
251   LexicalScope *PrevLexicalScope = nullptr;
252   for (SmallVectorImpl<InsnRange>::const_iterator RI = MIRanges.begin(),
253                                                   RE = MIRanges.end();
254        RI != RE; ++RI) {
255     const InsnRange &R = *RI;
256     LexicalScope *S = MI2ScopeMap.lookup(R.first);
257     assert(S && "Lost LexicalScope for a machine instruction!");
258     if (PrevLexicalScope && !PrevLexicalScope->dominates(S))
259       PrevLexicalScope->closeInsnRange(S);
260     S->openInsnRange(R.first);
261     S->extendInsnRange(R.second);
262     PrevLexicalScope = S;
263   }
264 
265   if (PrevLexicalScope)
266     PrevLexicalScope->closeInsnRange();
267 }
268 
269 /// getMachineBasicBlocks - Populate given set using machine basic blocks which
270 /// have machine instructions that belong to lexical scope identified by
271 /// DebugLoc.
272 void LexicalScopes::getMachineBasicBlocks(
273     const MDLocation *DL, SmallPtrSetImpl<const MachineBasicBlock *> &MBBs) {
274   MBBs.clear();
275   LexicalScope *Scope = getOrCreateLexicalScope(DL);
276   if (!Scope)
277     return;
278 
279   if (Scope == CurrentFnLexicalScope) {
280     for (const auto &MBB : *MF)
281       MBBs.insert(&MBB);
282     return;
283   }
284 
285   SmallVectorImpl<InsnRange> &InsnRanges = Scope->getRanges();
286   for (SmallVectorImpl<InsnRange>::iterator I = InsnRanges.begin(),
287                                             E = InsnRanges.end();
288        I != E; ++I) {
289     InsnRange &R = *I;
290     MBBs.insert(R.first->getParent());
291   }
292 }
293 
294 /// dominates - Return true if DebugLoc's lexical scope dominates at least one
295 /// machine instruction's lexical scope in a given machine basic block.
296 bool LexicalScopes::dominates(const MDLocation *DL, MachineBasicBlock *MBB) {
297   LexicalScope *Scope = getOrCreateLexicalScope(DL);
298   if (!Scope)
299     return false;
300 
301   // Current function scope covers all basic blocks in the function.
302   if (Scope == CurrentFnLexicalScope && MBB->getParent() == MF)
303     return true;
304 
305   bool Result = false;
306   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
307        ++I) {
308     if (const MDLocation *IDL = I->getDebugLoc())
309       if (LexicalScope *IScope = getOrCreateLexicalScope(IDL))
310         if (Scope->dominates(IScope))
311           return true;
312   }
313   return Result;
314 }
315 
316 /// dump - Print data structures.
317 void LexicalScope::dump(unsigned Indent) const {
318 #ifndef NDEBUG
319   raw_ostream &err = dbgs();
320   err.indent(Indent);
321   err << "DFSIn: " << DFSIn << " DFSOut: " << DFSOut << "\n";
322   const MDNode *N = Desc;
323   err.indent(Indent);
324   N->dump();
325   if (AbstractScope)
326     err << std::string(Indent, ' ') << "Abstract Scope\n";
327 
328   if (!Children.empty())
329     err << std::string(Indent + 2, ' ') << "Children ...\n";
330   for (unsigned i = 0, e = Children.size(); i != e; ++i)
331     if (Children[i] != this)
332       Children[i]->dump(Indent + 2);
333 #endif
334 }
335